This invention relates to optical transducers, and more particularly to optical transducers for detecting liquid level and the like.
FIGS. 1A-1C schematically depict a prior art optical transducer 10 for determining liquid level in tanks, vessels or the like. As shown, the transducer 10 includes an optical body 12 with a conical tip 14 at one end thereof, and a light source 16 and photosensor 18 at an opposite end thereof. In the absence of liquid as shown in FIG. 1A, light from the light source 16 is normally projected through the optical body 12 where it is internally reflected at a conical measuring surface 20 of the conical tip 14 and returns to the photosensor 18, as represented by arrow 22. When the conical tip 14 is submerged in liquid, as represented by dashed line 24 in FIG. 1B, the light is refracted out of the conical tip 14 and into the liquid (arrow 26). The amount of light at the photosensor 18 is thus significantly diminished. The presence or absence of liquid on the transducer 10, and thus the level of liquid in a tank, vessel or the like can be ascertained.
However, it has been found that liquid level transducers of above-described type can produce erroneous signals. As shown in FIG. 1C, when the liquid 24 descends to a level below the transducer 10, one or more liquid droplets 28 may form on the conical measuring surface 20 due to the surface tension of the liquid and the surface energy of the surface 20. Consequently, light is refracted out of the conical tip 14 and into the droplet(s) 28, as shown by arrow 26, to thereby give a false liquid level indication. This phenomena can occur whether the transducer 10 is in the horizontal position as shown, or in the vertical position.
In addition to the above, it has previously been difficult to construct a compact optical transducer that is capable of operating through a wide temperature range due to the relative proximity of the light source and photosensor to the liquid being measured.